| Disc brake is one of the basic braking devices of automobile, which thransforms the dynamic energy of automobile into heat energy and guarantees its safe operation by the action of the friction force produced by the friction material sliding on the friction disc. However, severe thermal recession of brake disc tends to happen at high speeds because of the limitation of friction materials, which will result the braking failure. The electromagnetic brake depends on the eddy current effect, which has a good effect at high-speed braking process. But it can not be used for parking location because it can not provide sufficient braking force at low-speed braking process but often used as auxiliary braking device. Since tribological researches have shown that magnetic field is beneficial for stabilizing friction behaviors and reducing wear rate, it is greatly significant to design an automotive magnetic-friction compound disc brake with the advantages of both frictional brake and electromagnetic brake, which also can take advantages of the beneficial effect of magnetic field on friction to improve the braking safety and reliability of vehicles.In this paper, in order to improve vehicle braking performance, an automotive magnetic-friction compound disc brake was designed and its braking performance was researched by methods of theoretical calculations, finite element simulations and test analysis. Firstly, based on the uniform design, magnetic conducting friction metarials with different formulations were prepared by the method of adding permalloy powder to organic friction material. Tribological properties and permeability of each material were studied by mesuring and analyzing its friction coefficient and wear rate. The optimal formula was obtained and prepared based on fuzzy theory and AHP and combined SPSS data processing software. What’s more, tribological properties, physical properties and permeability of the optimal formula were measured. Secondly, the structural parameters of automotive magnetic-friction compound disc brake was designed and calculated by considering the structures and working principles of both the friciton disc brake and electromagnetic brake. Based on the basic principles of electromagnetic field, the simulation model of the automotive magnetic-friction composite disc brake was established and its magnetic field and dynamic characteristic were simulated. The prototype of the automotive magnetic-friction composite disc brake was produced after finishing its design drawing. Finally, brake simulation experiments and friction surface microscopic analysis experiments were carried out, and variation rules and mechanisms of the brake torque, surface temperature of the brake disc and friction braking torque with the excitation voltage were explored. The results show that magnetic field mainly affects braking performance by changing the friction surface topography. With the increase of the excitation voltage, the mean braking torque increased gradually and the fluctuation of braking torque is obviously reduced obviously. Conclusively, the automotive magnetic-friction compound disc brake has a good braking performance. |
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